The immune response of cellular antigens in allograft rejection will be studied in dogs. Two different strains of in-bred Beagles will be used. The animals from two different strains will be operated upon in pairs and the distal portion of the right femur interchanged between the pairs. Presuming that the recipients become sensitized to the cellular antigens of the chondrocytes of the allograft, recipient lymphocytes will be isolated and reacted with donor chondrocytes, renal cells, and spleen cells labeled with Chromium-51. Humoral antibody will be obtained by ammonium-sulphate fractionation and its cytotoxic effects on the target cells will be noted as well. Studies will be performed to determine whether cellular antigens are present in the recipient synovium. Humoral antibody will be labeled with Rhodamine and reacted with the recipient synovium, the matrix antigens, GPL and PGS will be labeled with Fluorescein and counter-stained on the same synovial tissue. In order to determine which antigens are predominantly responsible for graft rejection, animals will be sensitized to donor lymphocytes and donor GPL and PGS. T-cells will be separated resulting in two separate colonies, one sensitized to the matrix antigens and the other to the cellular antigens. Allografting will be performed on two groups, following which one group will receive an intravenous infusion of T cells sensitized to cellular antigens and the other group an infusion of T cells sensitized against matrix antigens. The recipients will be observed for accelerated graft rejections. The effect of humoral antibody sensitized to matrix and cellular antigens in causing accelerated graft rejection will be studied in a similar fashion. Finally, attempts will be made to abolish the immune response employing immunosuppressive agents.